What is Open Gate video?
With Open Gate video, your recording device makes use of the full sensor size. You end up with the highest video file resolution your camera is technically capable of outputting. Normally, you would record in the UHD format with a resolution of 3,840 x 2,160 pixels in a 16:9 aspect ratio that uses a crop region on the sensor. I use the Open Gate mode on the Panasonic GH5, which has a 5K resolution of 4,992 x 3,744 pixels in a 4:3 aspect ratio.
The Open Gate feature was originally made for filming Anamorphic, a widescreen cinematography format with the use of Anamorphic lenses mostly used in Cinema movies. Anamorphic lenses produce an ultra-wide image that benefits from using the full sensor data. Most Spherical lenses do not have the same optics to produce such a wide image and do not produce visually distorted effects such as oval bokeh, horizontal flares, and image distortion. The higher resolution in the Open Gate recording mode brings some nice advantages to the post-production table which we get into.